Axle assembly having a wheel end disconnect and method of control

ABSTRACT

An axle assembly having a wheel end disconnect and a method of control. The axle assembly may include a friction clutch and a locking clutch that may be received in a hub assembly. The friction clutch may be moveable between an engaged position and a disengaged position. The locking clutch may be moveable between a locked position and an unlocked position and may actuate the friction clutch to the disengaged position.

TECHNICAL FIELD

This disclosure relates to an axle assembly having a wheel enddisconnect and a method of control.

BACKGROUND

An axle assembly having a wheel end disconnect unit is disclosed in U.S.Pat. No. 8,398,520.

SUMMARY

In at least one embodiment, an axle assembly is provided. The axleassembly may include a hub assembly, an axle shaft, a friction clutch,and a locking clutch. The hub assembly may be rotatable about an axis.The axle shaft may be received in the hub assembly and may be rotatableabout the axis. The friction clutch may be received in the hub assemblyand may be movable between an engaged position and a disengagedposition. Torque may be transmitted between the axle shaft and the hubassembly when the friction clutch is in the engaged position. Thelocking clutch may be received in the hub assembly and may be rotatableabout an axis with the axle shaft. The locking clutch may be movablebetween a locked position and an unlocked position. The locking clutchmay transmit torque between the axle shaft and the hub assembly when inthe locked position. The locking clutch may not transmit torque torotate the hub assembly when in the unlocked position.

In at least one embodiment, an axle assembly is provided. The axleassembly may include a hub assembly, a hub assembly, an axle shaft, afriction clutch, and a locking clutch. The hub assembly may be rotatableabout an axis. The axle shaft may be received in the hub assembly andmay be rotatable about the axis. The friction clutch may be configuredto transmit torque between the axle shaft and the hub assembly. Thefriction clutch may be moveable between an engaged position and adisengaged position. The locking clutch may be configured to transmittorque between the axle shaft and the hub assembly and may be moveablebetween a locked position and an unlocked position in which the lockingclutch does not transmit torque to rotate the hub assembly. The lockingclutch may actuate the friction clutch to the disengaged position whenthe locking clutch moves to the unlocked position.

In at least one embodiment, a method of controlling an axle assembly isprovided. The method may include disconnecting an axle shaft from a hubassembly that is adapted to support a wheel. A locking clutch may beactuated from a locked position in which the locking clutch transmitstorque to the hub assembly to an intermediate position in which thelocking clutch does not transmit torque between the axle shaft and thehub assembly. A friction clutch may be engaged and may transmit torquebetween the axle shaft and the hub assembly when the locking clutch isin the intermediate position. The locking clutch may be actuated fromthe intermediate position to an unlocked position in which the lockingclutch actuates the friction clutch from an engaged position to adisengaged position. Torque may be transmitted between the axle shaftand the hub assembly via the friction clutch when the friction clutch isin the engaged position. The friction clutch may not transmit sufficienttorque from the axle shaft to rotate the hub assembly when the frictionclutch is in the disengaged position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an axle assembly having a wheel enddisconnect.

FIG. 2 is a perspective view of a portion of FIG. 1 having the wheel enddisconnect.

FIGS. 3-5 comprise an exploded view of FIG. 2.

FIGS. 6-8 comprise an exploded view that depicts opposite sides of thecomponents shown in FIGS. 3-5.

FIG. 9 is a section view along section line 9-9 showing a locking clutchin a locked position and a friction clutch in an engaged position.

FIG. 10 is a section view showing the locking clutch in an intermediateposition and the friction clutch in the engaged position.

FIG. 11 is a section view showing the locking clutch in an unlockedposition and the friction clutch in a disengaged position.

FIG. 12 is a section view of another configuration of a wheel enddisconnect showing a locking clutch in a locked position and a frictionclutch in an engaged position.

FIG. 13 is a section view of the wheel end disconnect of FIG. 12 showingthe locking clutch in an unlocked position and the friction clutch inthe engaged position.

FIG. 14 is a section view of the wheel end disconnect of FIG. 12 showingthe locking clutch in an unlocked position and the friction clutch in adisengaged position.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

Referring to FIG. 1, an example of an axle assembly 10 is shown. Theaxle assembly 10 may be provided with a motor vehicle like a truck, bus,farm equipment, mining equipment, military transport or weaponryvehicle, or cargo loading equipment for land, air, or marine vessels.The motor vehicle may include a trailer for transporting cargo in one ormore embodiments.

The axle assembly 10 may be part of a vehicle drivetrain that mayprovide torque to one or more traction wheel assemblies that may includea tire mounted on a wheel. One or more axle assemblies may be providedwith the vehicle. For example, the axle assembly 10 may be part of atandem axle configuration or multi-axle configuration that may include aplurality of axle assemblies that may be connected in series. As is bestshown with reference to FIGS. 1 and 2, the axle assembly 10 may includea housing assembly 20, a differential assembly 22, at least one axleshaft 24, and a wheel end assembly 26.

Referring to FIG. 1, the housing assembly 20 may receive variouscomponents of the axle assembly 10. In addition, the housing assembly 20may facilitate mounting of the axle assembly 10 to the vehicle. Thehousing assembly 20 may include an axle housing 30 and a differentialcarrier 32.

The axle housing 30 may receive and support the axle shafts 24, whichare best shown in FIGS. 2 and 9. In at least one embodiment, the axlehousing 30 may include a center portion 40 and at least one arm portion42.

The center portion 40 may be disposed proximate the center of the axlehousing 30. The center portion 40 may define a cavity that may receivethe differential assembly 22. A lower region of the center portion 40may at least partially define a sump portion that may contain lubricant.Lubricant in the sump portion may be splashed by rotating components,such as a ring gear of the differential assembly 22. Splashed lubricantmay flow down the sides of the center portion 40 or may flow overinternal components of the axle assembly 10 and gather in the sumpportion.

The center portion 40 may include a carrier mounting surface. Thecarrier mounting surface may face toward and may engage the differentialcarrier 32. The carrier mounting surface may facilitate mounting of thedifferential carrier 32 to the axle housing 30. For example, the carriermounting surface may have a set of holes that may be aligned withcorresponding holes on the differential carrier 32. Each hole mayreceive a fastener, such as a bolt, that may couple the differentialcarrier 32 to the axle housing 30.

One or more arm portions 42 may extend from the center portion 40. Forexample, two arm portions 42 may extend in opposite directions from thecenter portion 40 and away from the differential assembly 22. The armportions 42 may have substantially similar configurations. For example,the arm portions 42 may each have a hollow configuration or tubularconfiguration that may extend around the corresponding axle shaft 24 andmay help separate or isolate the axle shaft 24 from the surroundingenvironment. An arm portion 42 or a portion thereof may be integrallyformed with the center portion 40. Alternatively, an arm portion 42 maybe separate from the center portion 40. In such a configuration, eacharm portion 42 may be attached to the center portion 40 in any suitablemanner, such as by welding or with one or more fasteners. Each armportion 42 may define an arm cavity that may receive a correspondingaxle shaft 24. In addition, each arm portion 42 may include a spindle44.

Referring to FIGS. 1 and 5, the spindle 44 may be disposed at an end ofeach arm portion 42 that may be disposed opposite the center portion 40.The spindle 44 may be integrally formed with the arm portion 42 or maybe provided as a separate component that is attached to an arm portion42. The spindle 44 may extend around or may be centered about an axis 50and may define a hole through which the axle shaft 24 may extend. Inaddition, the spindle 44 may rotatably support a hub of the wheel endassembly 26 as will be discussed in more detail below. In at least oneconfiguration, the spindle may include a threaded portion 46 that mayextend around an exterior surface of the spindle 44. The threadedportion 46 may be disposed proximate a spindle end surface 48 that maybe disposed at a distal end of the spindle 44.

Referring to FIG. 1, the differential carrier 32, which may also becalled a carrier housing, may be mounted on the center portion 40 of theaxle housing 30. The differential carrier 32 may rotatably support thedifferential assembly 22.

The differential assembly 22 may be disposed in the center portion 40 ofthe housing assembly 20. The differential assembly 22 may transmittorque to the vehicle traction wheel assemblies and permit the tractionwheel assemblies to rotate at different velocities. An abbreviateddiscussion of the operation of the differential assembly 22 follows withreference to FIG. 1.

An input yoke 60 may be coupled to a vehicle drivetrain component, suchas a drive shaft, that may be operatively connected to an output of avehicle transmission or transfer case, which in turn may receive torquefrom a vehicle power source, such as an engine or motor. Alternatively,the input yoke 60 may be operatively connected to an output of anotheraxle assembly. The input yoke 60 may be operatively connected to a drivepinion that may be disposed in the housing assembly 20. The drive pinionmay provide torque to a ring gear of the differential assembly 22. Thedifferential assembly 22 may be operatively connected to the axle shafts24 and may permit the axle shafts 24 to rotate at different rotationalspeeds in a manner known by those skilled in the art. As such, thedifferential assembly 22 may receive torque via the ring gear andprovide torque to the axle shafts 24.

Referring to FIGS. 2, 5 and 9, the axle shafts 24 may transmit torquefrom the differential assembly 22 to corresponding traction wheelassemblies. For example, two axle shafts 24 may be provided such thateach axle shaft 24 extends through a different arm portion 42 of axlehousing 30. The axle shafts 24 may extend along and may be rotatableabout the axis 50 by the differential assembly 22. Each axle shaft 24may have a first end and a second end. The first end may be operativelyconnected to the differential assembly 22. The second end may bedisposed opposite the first end and may be operatively connected to acorresponding wheel end assembly 26. In at least one configuration, thesecond end may include an axle recess 62 an axle spline 64, a firstgroove 66, and a second groove 68 as is best shown in FIG. 5.

The axle recess 62 may be disposed along the axis 50. The axle recess 62may be configured as a blind hole that may extend from an end surface ofthe axle shaft 24 toward the first end and the differential assembly 22.

The axle spline 64 may be disposed opposite the axle recess 62. The axlespline 64 may include a plurality of teeth that may be arranged aroundan exterior surface or outside circumference of the axle shaft 24. Theteeth may be disposed substantially parallel to the axis 50.

The first groove 66 and the second groove 68 may be provided in the axlespline 64. For example, the first groove 66 and the second groove 68 mayeach have an annular configuration in which the first groove 66 and thesecond groove 68 may extend continuously around the axis 50. Inaddition, the first groove 66 and the second groove 68 may extend in aradial direction toward the axis 50 such that the first groove 66 andthe second groove 68 may extend at least partially through the teeth ofthe axle spline 64. The first groove 66 may be disposed substantiallyparallel to the second groove 68 and may be spaced apart from the secondgroove 68. For example, the first groove 66 may be axially positionedcloser to the end surface of the axle shaft 24 than the second groove68. In at least one configuration, the first groove 66 may extend aroundthe axle recess 62 while the second groove 68 may not extend around theaxle recess 62.

Referring to FIGS. 1 and 2, wheel end assemblies 26 may be mounted atopposing ends of the housing assembly 20. The wheel end assembly 26 mayfacilitate mounting and rotation of a vehicle wheel 70, which is bestshown in FIG. 9. In addition, the wheel end assembly 26 may beselectively connectable to and disconnectable from a corresponding axleshaft 24 as will be discussed in more detail below. In at least oneconfiguration such as is shown in FIGS. 3-5, the wheel end assembly 26may include a first wheel bearing 80, a second wheel bearing 82, apreload nut 84, a seal assembly 86, a hub assembly 88, a friction clutch90, a locking clutch 92, a locking clutch actuator 94, a first biasingmember 96, and a second biasing member 98.

The components associated with selectively connecting and disconnectingthe wheel end assembly 26 from a corresponding axle shaft 24 may bereferred to as a wheel end disconnect. For instance, components such asthe friction clutch 90, locking clutch 92, locking clutch actuator 94,first biasing member 96, and second biasing member 98 may allow torqueto be transmitted between the axle shaft 24 and its corresponding hubassembly 88 that is sufficient to rotate the hub assembly 88 when thewheel end disconnect is connected or in a connected condition and maynot allow torque to be transmitted between the axle shaft 24 and itscorresponding hub assembly 88 that is sufficient to rotate the hubassembly 88 when disconnected or in a disconnected condition.

Referring to FIGS. 5, 8 and 9, the first wheel bearing 80 may bedisposed on the spindle 44 and may rotatably support the hub assembly88. For example, the first wheel bearing 80 may be disposed on and mayextend around the external surface of the spindle 44 and may be receivedinside the hub assembly 88. The first wheel bearing 80 may be positionedcloser to the spindle end surface 48 than the second wheel bearing 82.The first wheel bearing 80 may have any suitable configuration. Forinstance, the first wheel bearing 80 may include a plurality of rollingelements, such as balls or rollers, that may be disposed between aninner race and an outer race. The inner race may be disposed on and mayextend around an external surface or outside circumferential surface ofthe spindle 44. The outer race may be disposed on the hub assembly 88and may extend around the inner race.

The second wheel bearing 82 may also be disposed on the spindle 44 andmay rotatably support the hub assembly 88. For example, the second wheelbearing 82 may be disposed on and may extend around the external surfaceof the spindle 44 and may be received inside the hub assembly 88. Thesecond wheel bearing 82 may be spaced apart from the first wheel bearing80 and may be positioned closer to the differential assembly 22 than thefirst wheel bearing 80. The second wheel bearing 82 may have anysuitable configuration. For instance, the second wheel bearing 82 mayinclude a plurality of rolling elements, such as balls or rollers, thatmay be disposed between an inner race and an outer race.

Referring to FIGS. 4, 7 and 9, the preload nut 84 may help secure thefirst wheel bearing 80. More specifically, the preload nut 84 mayinhibit or limit axial movement of the first wheel bearing 80 along thespindle 44 in a direction that extends toward the spindle end surface48. For example, the preload nut 84 may receive and may mate withcorresponding threads of the threaded portion 46 of the spindle 44. Thepreload nut 84 may engage the inner race of the first wheel bearing 80and may be tightened to exert a preload force on the first wheel bearing80 or the first wheel bearing 80 and the second wheel bearing 82. Forinstance, a spacer 100, which is shown in FIGS. 5, 8 and 9, may extendfrom the inner race of the first wheel bearing 80 to the inner race ofthe second wheel bearing 82. As such, the spacer 100 may keep the innerraces at a substantially constant axial distance from each other andfacilitate the transmission of preload force. The preload nut 84 may besecured with one or more fasteners 102, such as a snap ring, screw, boltor combinations thereof, to inhibit the preload nut 84 from rotating orloosening. A key may be provided on the fastener 102 that may bereceived in a corresponding key slot in the spindle 44 to inhibitrotation of the fastener 102.

Referring to FIGS. 5, 8 and 9, the seal assembly 86 may be disposedbetween the hub assembly 88 and the spindle 44. For example, the sealassembly 86 may extend continuously around the axis 50 and the spindle44 and may extend from the spindle 44 to the hub assembly 88. The sealassembly 86 may help inhibit lubricant from exiting the hub assembly 88and may inhibit contaminants from entering the hub assembly 88.

Referring to FIGS. 2 and 9, the hub assembly 88 may be rotatablydisposed on the spindle 44. As such, the hub assembly 88 may berotatable about the axis 50 with respect to the spindle 44. In at leastone configuration, the hub assembly 88 may include a hub cap 110, afirst hub portion 112, a second hub portion 114, a third hub portion116, and a hub cavity 118.

Referring to FIGS. 2, 3, 6 and 9, the hub cap 110 may be disposed atdistal end of the hub assembly 88. The hub cap 110 may enclose an end ofthe hub assembly 88 that may be located near the distal end of the axleshaft 24. The hub cap 110 may be fastened to the first hub portion 112in any suitable manner, such as with one or more fasteners, such asbolts or mounting studs. In at least one configuration, a set ofmounting studs 120 are arranged around the axis 50 and extend throughcorresponding openings in the hub cap 110. The hub cap 110 may befurther secured with nuts 122 and washers 124 that may receive themounting studs 120.

Referring to FIGS. 4, 7 and 9, the hub cap 110 may be integrally formedwith or may receive a guide pin 126. The guide pin 126 may extend alongthe axis 50 toward the axle shaft 24 and may be received in the axlerecess 62 to rotatably support the axle shaft 24. A support bearing 128,such as a roller bearing, may be disposed in the axle recess 62 and mayextend around the guide pin 126 to help align and rotatably support theaxle shaft 24. A thrust bearing 130 and optionally a washer 132 may beprovided between the hub cap 110 and the end of the axle shaft 24 tofacilitate rotation of the axle shaft 24 with respect to the hub cap110.

Referring to FIGS. 2, 3, 6, and 9, the first hub portion 112 may receivethe friction clutch 90. In at least one configuration, the first hubportion 112 may extend around the friction clutch 90 and may extend inan axial direction that may extend along the axis 50 from the hub cap110 to the second hub portion 114. For example, the first hub portion112 may have a first end surface 140 and a second end surface 142. Thefirst end surface 140 may engage the hub cap 110. The second end surface142 may be disposed opposite the first end surface 140 and may engagethe second hub portion 114. The first hub portion 112 may also include aset of holes 144, at least one slot 146, and one or more alignment pinopenings 148.

The set of holes 144 may extend from the first end surface 140 towardthe second end surface 142. In the configuration shown, the set of holes144 are configured as through holes that extend from the first endsurface 140 to the second end surface 142 to allow a mounting stud 120to extend through the first hub portion 112.

One or more slots 146 may extend radially outward from an interiorsurface of the first hub portion 112. A slot 146 may receive acorresponding tab on a disc that may be provided with the frictionclutch 90 as will be discussed in more detail below. For example, aplurality of slots 146 may be provided that may be arranged around theaxis 50 and may be spaced apart from each other. Each slot 146 mayextend between the first end surface 140 and the second end surface 142such that the slots 146 may be extend in an axial direction and mayextend substantially parallel to the axis 50.

Referring to FIG. 6, one or more alignment pin openings 148 may extendfrom the second end surface 142. An alignment pin opening 148 mayreceive a corresponding alignment pin 150, which is best shown in FIGS.4 and 7, that may be received in a corresponding alignment pin openingon the second hub portion 114 to help align the first hub portion 112and the second hub portion 114.

Referring to FIGS. 2, 4, 7, and 9, the second hub portion 114 mayreceive at least a portion of the locking clutch 92, the locking clutchactuator 94, or both. The second hub portion 114 may be a separatecomponent from the first hub portion 112; however, it is contemplatedthat the first hub portion 112 may be integrally formed with the secondhub portion 114 in one or more embodiments. In at least oneconfiguration, the second hub portion 114 may extend around the lockingclutch 92, the locking clutch actuator 94, or both, and may extend in anaxial direction from the first hub portion 112 to the third hub portion116. For example, the second hub portion 114 may have a first endsurface 160 and a second end surface 162. The first end surface 160 mayengage the second end surface 142 of the first hub portion 112. Thesecond end surface 162 may be disposed opposite the first end surface160 and may engage the third hub portion 116. The second hub portion 114may also include a set of holes 164, a hub gear 166, and one or morealignment pin openings 168.

Referring to FIGS. 4 and 7, the set of holes 164 may extend from thefirst end surface 160 toward the second end surface 162. In theconfiguration shown, the set of holes 164 are configured as throughholes that extend from the first end surface 160 to the second endsurface 162 to allow a mounting stud 120 to extend through the secondhub portion 114.

Referring to FIGS. 4, 7, and 9, a hub gear 166 may extend from thesecond hub portion 114. For example, the hub gear 166 may be configuredas a face gear that may include a set of teeth that may extend from thefirst end surface 160 in a direction that extends away from the secondend surface 162. Alternatively, the hub gear 166 may be configured as aspline or set of teeth that may be disposed in the second hub portion114 and that may extend toward the axis 50. The set of teeth may bearranged around the axis 50 and optionally around the locking clutchactuator 94 and may extend from an inside circumference of the secondhub portion 114. As such, the hub gear 166 may be disposed closer to theaxis 50 than the holes 164. The teeth of the hub gear 166 may beselectively engaged by the locking clutch 92 as will be discussed inmore detail below.

Referring to FIG. 4, one or more alignment pin openings 168 may extendfrom the first end surface 160. For example, an alignment pin opening168 that is provided with the first end surface 160 may receive acorresponding alignment pin 150 to help align the first hub portion 112and the second hub portion 114.

Referring to FIGS. 2, 5, 8, and 9, the third hub portion 116 may receiveat least a portion of the spindle 44, the locking clutch actuator 94, orboth. The third hub portion 116 may be a separate component from thesecond hub portion 114; however, it is contemplated that the second hubportion 114 may be integrally formed with the second hub portion 114 inone or more embodiments. In at least one configuration, the third hubportion 116 may extend around and may be spaced apart from the spindle44, the locking clutch actuator 94, or both, and may be disposed on anopposite side of the second hub portion 114 from the first hub portion112. For example, the third hub portion 116 may have a first end surface170 and a second end surface 172. The first end surface 170 may engagethe second end surface 162 of the second hub portion 114. The second endsurface 172 may be disposed opposite the first end surface 170. Thesecond hub portion 114 may also include a set of holes 174 and a hubmounting flange 176.

Referring to FIGS. 5 and 9, the set of holes 174 may extend from thefirst end surface 170 toward the second end surface 172. In theconfiguration shown, the set of holes 174 are configured as blind holesthat receive mounting studs 120. The mounting studs 120 may be fixedlypositioned with respect to the third hub portion 116. For instance, theset of holes 174 may have threads that may mate with correspondingthreads on the mounting studs 120.

Referring to FIGS. 2, 5 and 9, the hub mounting flange 176 may extendaway from the axis 50. For instance, the hub mounting flange 176 mayextend substantially perpendicular to the axis 50 in one or moreconfigurations. The hub mounting flange 176 may facilitate mounting of awheel 70 that may support a tire. For example, the hub mounting flange176 may include a set of mounting lug fastener holes that may eachreceive a wheel mounting lug 180. As is best shown in FIG. 9, the wheel70 may have a wheel mounting flange that may have a set of holes thatmay be aligned with the wheel mounting lugs 180. A lug nut 182 may bethreaded onto each wheel mounting lug 180 to secure the wheel 70 to thehub assembly 88.

Referring to FIG. 9, the hub cavity 118 may be disposed inside the hubassembly 88 and may extend between opposing ends of the hub assembly 88.For example, the hub cavity 118 may extend from the hub cap 110 to theseal assembly 86. The hub cavity 118 may receive at least a portion ofan axle shaft 24 and may receive at least a portion of variouscomponents of the wheel end assembly 26, such as the spindle 44, firstwheel bearing 80, the second wheel bearing 82, the preload nut 84, theseal assembly 86, the friction clutch 90, the locking clutch 92, thelocking clutch actuator 94, the first biasing member 96, and the secondbiasing member 98.

Referring to FIGS. 4, 7 and 9, the friction clutch 90 may be adapted toprovide friction that may allow the axle shaft 24 and the hub assembly88 to achieve sufficiently similar rotational velocities about the axis50 or synchronize the rotational velocities of the axle shaft 24 and thehub assembly 88 about the axis 50. In at least one configuration, thefriction clutch 90 may include a disc pack 190, a disc pack hub 192, anactuation plate 194, and a retainer 196.

The disc pack 190 may be axially positioned between the actuation plate194 and the locking clutch 92. In addition, the disc pack 190 may beradially positioned between the disc pack hub 192 and a portion of thehub assembly 88, such as the first hub portion 112. The disc pack 190may include one or more inner friction discs 200 and one or more outerfriction discs 202.

One or more inner friction discs 200 may be disposed on the disc packhub 192 and may extend radially away from the axis 50. For example, theinner friction discs 200 may have a hole that may receive the disc packhub 192. The hole in an inner friction disc 200 may have a toothedprofile that may engage and mate with a set of teeth on the disc packhub 192 such that the inner friction disc 200 is rotatable about theaxis 50 with the disc pack hub 192.

One or more outer friction discs 202 may be disposed adjacent to aninner friction disc 200. The outer friction discs 202 may be spacedapart from each other such that an inner friction disc 200 may bedisposed between adjacent outer friction discs 202. The outer frictiondiscs 202 may extend from the hub assembly 88 toward the axis 50 and maynot rotate about the axis 50 with respect to the hub assembly 88. Forexample, the outer friction discs 202 may extend from the first hubportion 112 toward the disc pack hub 192. The outer friction discs 202may have an inside circumferential surface that may face toward and mayextend around the axis 50 such that the inner circumferential surfacemay be spaced apart from the disc pack hub 192. As is best shown inFIGS. 4 and 7, the outer friction discs 202 may have one or more tabs204 that may extend away from the axis 50 and may extend away from anouter surface or outside circumference of the outer friction disc 202. Atab 204 may be received in a corresponding slot 146 in the first hubportion 112 180. As such, a tab 204 may cooperate with a slot 146 toinhibit rotation of the outer friction discs 202 with respect to thefirst hub portion 112 while allowing deflection or limited axialmovement of the outer friction discs 202.

The disc pack hub 192 may be received inside the disc pack 190. The discpack hub 192 may be axially positioned between the actuation plate 194and the locking clutch 92 and may be radially positioned between theaxle shaft 24 and the disc pack 190. In at least one configuration, thedisc pack hub 192 may include a first side surface 210, a second sidesurface 212, an inner surface 214, a set of disc pack hub teeth 216, andone or more fastener holes 218.

The first side surface 210 may face toward and may engage the actuationplate 194. The first side surface 210 may be disposed substantiallyperpendicular to the axis 50 in one or more configurations.

The second side surface 212 may be disposed opposite the first sidesurface 210. The second side surface 212 may face toward the lockingclutch 92 and may be selectively engaged by the locking clutch 92.

The inner surface 214 may extend from the first side surface 210 to thesecond side surface 212. The inner surface 214 may face toward the axleshaft 24 and may define a hole through which the axle shaft 24 mayextend. The inner surface 214 may be spaced apart from the axle shaft24.

The set of disc pack hub teeth 216 may be disposed opposite the innersurface 214. The disc pack hub teeth 216 may be arranged around the axis50 and may extend away from the axis 50. In addition, the disc pack hubteeth 216 may extend between the first side surface 210 and the secondside surface 212. The disc pack hub teeth 216 may mesh with the toothedprofile of the inner friction discs 200 to inhibit rotation of the innerfriction discs 200 about the axis 50 with respect to the disc pack hub192. The disc pack hub teeth 216 may be spaced apart from and may notengage the outer friction discs 202.

One or more fastener holes 218 may be provided with the disc pack hub192. For instance, one or more fastener holes 218 may extend from thefirst side surface 210 toward the second side surface 212. Each fastenerhole 218 may receive a corresponding fastener 220, such as a bolt, thatmay couple the disc pack hub 192 to the actuation plate 194. As such,the disc pack hub 192 may not rotate about the axis 50 with respect tothe actuation plate 194.

The actuation plate 194 may be disposed adjacent to the disc pack 190and the disc pack hub 192. The actuation plate 194 may be axiallypositioned between the first biasing member 96 and the disc pack 190 andmay be radially positioned between the axle shaft 24 and the hubassembly 88. In addition, the actuation plate 194 may be rotatable aboutthe axis 50 with the axle shaft 24. In at least one configuration, theactuation plate 194 may include an outboard side surface 230, an inboardside surface 232, and actuation plate spline 234, and one or morefastener holes 236.

The outboard side surface 230 may face toward the hub cap 110 and mayengage the first biasing member 96.

The inboard side surface 232 may be disposed opposite the outboard sidesurface 230. The inboard side surface 232 may face toward the disc pack190 and may engage the first side surface 210 of the disc pack hub 192.The inboard side surface 232 may selectively engage the disc pack 190 aswill be discussed in more detail below.

The actuation plate spline 234 may extend between the outboard sidesurface 230 and the inboard side surface 232. The actuation plate spline234 may include a plurality of teeth that may be arranged around theaxle shaft 24 and that may extend toward the axle shaft 24. The teethmay be disposed substantially parallel to the axis 50 and may mate withthe teeth of the axle spline 64. As such, the actuation plate spline 234may cooperate with the axle spline 64 to inhibit rotation of theactuation plate 194 about the axis 50 with respect to the axle shaft 24while allowing the actuation plate 194 to move axially or along the axis50 with respect to the axle shaft 24.

One or more fastener holes 236 may be provided with the actuation plate194. For instance, one or more fastener holes 236 may extend from theoutboard side surface 230 to the inboard side surface 232. Each fastenerhole 236 may be aligned with a corresponding fastener hole 218 on thedisc pack hub 192 may receive a corresponding fastener 220.

The retainer 196 may be disposed at an opposite end of the disc pack 190from the actuation plate 194. As such, the retainer 196 may be axiallypositioned between the disc pack 190 and the locking clutch 92. Theretainer 196 may be fixedly positioned with respect to the hub assembly88. For example, the retainer 196 may be fixedly mounted in the firsthub portion 112 and may extend toward the axis 50. The retainer 196 mayhave any suitable configuration. For example, the retainer 196 may beconfigured as an end plate, washer, snap ring, or one or moreprotrusions that may extend from the hub assembly 88 toward the axis 50.The retainer 196 may act as a stop that may inhibit axial movement ofthe disc pack 190 toward the locking clutch 92, or to the right from theperspective shown in FIG. 9. In at least one configuration, the retainer196 may directly engage an end plate of the disc pack 190 or an outerfriction disc 202 that is located at an end of the disc pack 190 that islocated closest to the locking clutch 92.

Referring to FIGS. 4, 7 and 9, the locking clutch 92 may be rotatableabout the axis 50 with a corresponding axle shaft 24. The locking clutch92 may be configured to selectively engage the hub assembly 88 tomechanically interlock the axle shaft 24 and the hub assembly 88. Inaddition, the locking clutch 92 may selectively engage the frictionclutch 90 to actuate the friction clutch 90 as will be discussed in moredetail below. The locking clutch 92 may be axially positioned betweenthe friction clutch 90 and the locking clutch actuator 94. In at leastone configuration, the locking clutch 92 may include a locking clutchspline 240, a locking clutch gear 242, an inner pocket 244, an outerpocket 246, and an engagement feature 248.

The locking clutch spline 240 may include a plurality of teeth that maybe arranged around the axle shaft 24 and that may extend toward the axleshaft 24. The teeth may be disposed substantially parallel to the axis50 and may mate with the teeth of the axle spline 64. As such, thelocking clutch spline 240 may cooperate with the axle spline 64 toinhibit rotation of the locking clutch 92 about the axis 50 with respectto the axle shaft 24 while allowing the locking clutch 92 to moveaxially with respect to the axle shaft 24. The locking clutch spline 240may also be radially positioned between axle shaft 24 and a portion ofthe locking clutch actuator 94, such as a piston of the locking clutchactuator 94.

The locking clutch gear 242 may be disposed proximate an outsidecircumference of the locking clutch 92. For example, the locking clutchgear 242 may be configured as a face gear that may include a set ofteeth that may extend in an axial direction away from the frictionclutch 90 and toward the hub gear 166 of the hub assembly 88. The set ofteeth may be arranged around the axis 50 and may extend around and mayat least partially define the outer pocket 246. Alternatively, thelocking clutch gear 242 may be configured as a spline or set of teeththat may be disposed opposite the locking clutch spline 240 and that mayextend away from the axis 50. The set of teeth of the locking clutchgear 242 may selectively engage the teeth of the hub gear 166 as will bediscussed in more detail below.

The inner pocket 244 may extend around the axle shaft 24. The innerpocket 244 may be configured as a recess that may extend from anoutboard side of the locking clutch 92 in an axial direction thatextends away from the friction clutch 90. The inner pocket 244 mayreceive a portion of the second biasing member 98.

The outer pocket 246 may be disposed on an opposite side of the lockingclutch 92 from the inner pocket 244 and may be disposed further from theaxis 50 than the inner pocket 244. The outer pocket 246 may extendaround at least a portion of the locking clutch spline 240 and mayreceive a portion of the locking clutch actuator 94 in one or moreembodiments.

Referring to FIGS. 4 and 9, the engagement feature 248 may face towardand may selectively engage the friction clutch 90. For example, theengagement feature 248 may face toward and may selectively engage thesecond side surface 212 of the disc pack hub 192. In the configurationshown, the engagement feature 248 is configured as a ring that mayextend around the axis 50 and may protrude an axial direction toward thefriction clutch 90.

Referring to FIGS. 4, 7 and 9, the locking clutch actuator 94 may beoperable to actuate the locking clutch 92 toward the friction clutch 90or to the left from the perspective shown in FIG. 9. More specifically,the locking clutch actuator 94 may actuate the locking clutch 92 from alocked position to an unlocked position and to an intermediate positionthat may be disposed between the locked position and the unlockedposition as will be discussed in more detail below. The locking clutchactuator 94 may be fixedly mounted to a portion of the housing assembly20, such as the spindle 44. In such a configuration, the locking clutchactuator 94 may not rotate about the axis 50 and may be spaced apartfrom the hub assembly 88. The locking clutch actuator 94 may be of anysuitable type. For example, the locking clutch actuator 94 may be apneumatic, hydraulic, electrical, or electromechanical actuator. In theconfiguration shown, the locking clutch actuator is depicted as apneumatic actuator that may include a piston housing 250 and one or morepistons 252.

The piston housing 250 may be received inside the hub assembly 88 andmay be fixedly disposed on the housing assembly 20. The piston housing250 may have an annular configuration and may extend continuously aroundthe axle shaft 24. In addition, the piston housing 250 may define one ormore recesses that may receive one or more pistons 252. In at least oneconfiguration, a single recess may be provided that may receive acorresponding piston 252. The single recess may or may not extendcontinuously around the axis 50. In the configuration shown, the recessis depicted as an annular recess that extends continuously around theaxis 50 and is open in a direction that faces toward the locking clutch92. The piston housing 250 may also include a passage 254, which is bestshown in FIG. 9, that may be selectively fluidly connected to apressurized gas source 256, such as via a conduit like a tube or hose.Pressurized gas may flow from the pressurized gas source 256 through thepassage 254 and to the recess and may exert force on a piston 252 toactuate the piston 252 toward the friction clutch 90, or to the leftfrom the perspective shown in FIG. 9. Pressurized gas may be vented fromthe passage 254 and hence from the recess to allow the piston 252 tomove away from the friction clutch 90, or to the right from theperspective shown in FIG. 9.

One or more pistons 252 may be movably disposed on the piston housing250. More specifically, a piston 252 may be movable in an axialdirection with respect to the piston housing 250. In the configurationshown, a single piston 252 is provided that has an annular configurationthat may extend continuously around the axis 50; however, it is alsocontemplated that the piston may also be configured to not extendcontinuously around the axis 50. The piston 252 may have a first endsurface and a second end surface that may be disposed opposite the firstend surface. The first end surface may face toward the locking clutch92. The second end surface may face away from locking clutch 92 and maybe received in the recess. One or more seals 258 may be provided withthe piston 252, the piston housing 250, or both, to inhibit the leakageof fluid between the piston 252 and the piston housing 250.

A thrust bearing 260 may be provided between the locking clutch 92 and apiston 252. For example, the thrust bearing 260 may be axiallypositioned between the locking clutch 92 and the first end of the piston252. The thrust bearing 260 may facilitate rotation of the lockingclutch 92 with respect to the piston 252

The first biasing member 96 may bias the actuation plate 194 toward thelocking clutch 92. As such, the first biasing member 96 may urge thefriction clutch 90 toward an engaged position in which the actuationplate 194 compresses the disc pack 190 to engage the inner frictiondiscs and outer friction discs, such as in an axial direction to theright from the perspective shown in FIG. 9. The first biasing member 96may be of any suitable type. For example, the first biasing member 96may be configured as a diaphragm washer, one or more springs, or thelike. As is best shown in FIG. 9, the first biasing member 96 may beaxially positioned between the hub cap 110 and the actuation plate 194and may actuate the friction clutch 90 toward the engaged position whensufficient force is not exerted by the locking clutch 92 against thefriction clutch 90. The first biasing member 96 may extend axially fromthe actuation plate 194 to a retainer feature 270, such as a washer,snap ring or combination thereof, that may be received in the firstgroove 66 of the axle shaft 24.

The second biasing member 98 may bias the locking clutch 92 toward thehub gear 166 of the hub assembly 88. More specifically, the secondbiasing member 98 may actuate the locking clutch 92 toward the lockedposition when sufficient force is not exerted by the locking clutchactuator 94. As such, the second biasing member 98 may urge the lockingclutch 92 toward a locked position in which the locking clutch gear 242of the locking clutch 92 meshes with the hub gear 166 of the hubassembly 88, or in an axial direction to the right from the perspectiveshown in FIG. 9. The second biasing member 98 may be located at anopposite side of the actuation plate 194 from the first biasing member96 and may be axially positioned between the actuation plate 194 and thelocking clutch 92. In addition, the second biasing member 98 may extendfrom the locking clutch 92 toward the actuation plate 194. The secondbiasing member 98 may be of any suitable type. For example, the secondbiasing member 98 may be configured as one or more springs or the like.In at least one configuration, the second biasing member 98 may beconfigured as a spring that may extend around the axle shaft 24 and mayextend from the locking clutch 92 to a retainer feature 272, such as awasher, snap ring or combination thereof, that may be received in thesecond groove 68 of the axle shaft 24. Accordingly, the second biasingmember 98 may be spaced apart from and may not engage the frictionclutch 90 and may not exert a biasing force on the friction clutch 90.

Referring to FIGS. 9-11, a method of control and operation of the wheelend assembly 26 will now be described in more detail. As an overview,the friction clutch 90 and the locking clutch 92 may be operable todisconnect an axle shaft 24 from a corresponding hub assembly 88 suchthat no torque or negligible torque is transmitted between the axleshaft 24 to the hub assembly 88. In addition, the friction clutch 90 andthe locking clutch 92 may cooperate to connect an axle shaft 24 to acorresponding hub assembly 88 so that torque may be transmitted betweenthe axle shaft 24 and the hub assembly 88 or from the axle shaft 24 tothe hub assembly 88. More specifically, the friction clutch 90 may beengaged to allow the axle shaft 24 and the hub assembly 88 to rotatetogether about the axis 50 to obtain the same or substantially similarrotational velocities prior to locking the locking clutch 92 to the hubassembly 88 to more robustly transmit torque between the axle shaft 24and the hub assembly 88 by way of the locking clutch 92.

The friction clutch 90 may be movable between an engaged position and adisengaged position. The locking clutch 92 may be movable between threepositions, which are referred to as a locked position, an intermediateposition, and an unlocked position. The intermediate position may beaxially positioned between the locked position and the unlockedposition.

Referring to FIG. 9, the axle assembly 10 is shown with the frictionclutch 90 in an engaged position and the locking clutch 92 in a lockedposition. Torque may be transmitted between the axle shaft 24 and thehub assembly 88 via the friction clutch 90 when the friction clutch 90is in the engaged position. In the engaged position, the locking clutch92 is spaced apart from the friction clutch 90 under the biasing forceof the second biasing member 98 and the first biasing member 96 exerts abiasing force on the actuation plate 194 that actuates the actuationplate 194 toward the locking clutch 92 to compress and engage the discpack 190. Torque may also be transmitted between the axle shaft 24 andthe hub assembly 88 via the locking clutch 92 when the locking clutch 92is in the locked position. In the locked position, the second biasingmember 98 exerts a biasing force on the locking clutch 92 that actuatesthe locking clutch 92 away from the friction clutch 90 so that thelocking clutch gear 242 meshes with the hub gear 166 of the hub assembly88. As such, torque may be transmitted between the axle shaft 24 and thehub assembly 88 by way of the meshed teeth of the locking clutch gear242 and the hub gear 166. The locking clutch actuator 94 may be disposedin a retracted position in which the locking clutch actuator 94 does notexert sufficient force on the locking clutch 92 to overcome the biasingforce of the second biasing member 98, such as when pressurized gas isnot provided to the piston housing 250.

Referring to FIG. 10, the axle assembly 10 is shown with the frictionclutch 90 in the engaged position and the locking clutch 92 in theintermediate position. In the intermediate position, the locking clutchactuator 94 is actuated toward the friction clutch 90 or to the leftfrom the perspective shown such that (1) the locking clutch gear 242disengages from the hub gear 166 of the hub assembly 88 and (2) thelocking clutch 92 does not actuate the friction clutch 90 from itsdisengaged position. As such, torque may not be transmitted between theaxle shaft 24 and the hub assembly 88 via the locking clutch 92 when thelocking clutch 92 is in the intermediate position. For example, apredetermined amount of pressurized fluid may be provided to actuate thepiston 252 from its retracted position such that the locking clutch 92moves from the locked position to the intermediate position withoutreaching the unlocked position. The locking clutch 92 may or may notengage the friction clutch 90 when the locking clutch 92 is in theintermediate position. Moreover, the friction clutch 90 may not beactuated by the locking clutch 92 in the intermediate position. As such,torque may not be transmitted between the axle shaft 24 and the hubassembly 88 via the friction clutch 90.

Referring to FIG. 11, the axle assembly 10 is shown with the frictionclutch 90 in a disengaged position and the locking clutch 92 in theunlocked position. Torque may not be transmitted between the axle shaft24 and the hub assembly 88 via the friction clutch 90 when the frictionclutch 90 is in the disengaged position or insufficient torque may betransmitted between the axle shaft 24 and the hub assembly 88 via thefriction clutch 90 to rotate the hub assembly 88 when the frictionclutch 90 is in the disengaged position. In the disengaged position, thelocking clutch 92 may engage the friction clutch 90 and may overcome thebiasing force exerted by the first biasing member 96 and the secondbiasing member 98 to actuate the disc pack hub 192 and the actuationplate 194 toward the hub cap 110, or to the left from the perspectiveshown in FIG. 11, to decompress, release, or disengage the discs of thedisc pack 190. As such, no torque or insufficient torque may betransmitted between the axle shaft 24 and the hub assembly 88 via thefriction clutch 90 when the friction clutch 90 is in the disengagedposition. For example, an additional amount of pressurized fluid may beprovided to further actuate the piston 252 to move the locking clutch 92from the intermediate position to the unlocked position, or further tothe left from the perspective shown as compared to FIG. 10. As such, thelocking clutch 92 may engage or contact the disc pack hub 192 of thefriction clutch 90, compress the second biasing member 98, and exertforce on the disc pack hub 192 to actuate the friction clutch 90 to thedisengaged position. The actuation plate 194 may move away from theretainer 196 to allow the discs of the disc pack 190 to move apart andmay compress the first biasing member 96. As such, the hub assembly 88may be rotatable with respect to the axle shaft 24 when the frictionclutch 90 is in the disengaged position and the locking clutch 92 is inthe unlocked position.

The axle shaft 24 may be reconnected to the hub assembly 88 byeffectively reversing the sequence of steps described above. Forinstance, pressurized gas may be vented to allow the piston 252 toretract and the locking clutch 92 to return to the intermediate positionunder the biasing force of the second biasing member 98. Movement of thelocking clutch 92 to the intermediate position may reduce or eliminatethe force exerted by the locking clutch 92 against the disc pack hub192. The disc pack hub 192 and actuation plate 194 may then move fromthe disengaged position to the engaged position to compress and reengagethe discs of the disc pack 190 under the biasing force of the firstbiasing member 96. As a result, torque may be transmitted between theaxle shaft 24 and the hub assembly 88 via the friction clutch 90. Thelocking clutch 92 may be held in the intermediate position before movingto the locked position. For instance, the locking clutch 92 may be heldin the intermediate position until the rotational velocity of the hubassembly 88 is sufficiently close to the rotational velocity of the axleshaft 24. The rotational velocity of the hub assembly 88 may besufficiently close to the rotational velocity of the axle shaft 24 whenthe rotational velocity of the hub assembly 88 is within a thresholdamount from the rotational velocity of the axle shaft 24. The thresholdamount may represent a tolerance or velocities at which the lockingclutch gear 242 is re-engageable with the hub gear 166 of the hubassembly 88. For instance, the threshold amount may be when therotational velocities are about 5% or less from each other.Alternatively, a rotational velocity of the hub assembly 88 that issufficiently close the rotational velocity of the axle shaft 24 may beobtained by holding the locking clutch 92 in the intermediate positionfor a predetermined period of time. The threshold amount orpredetermined period of time may be based on system performancerequirements or determined by vehicle development testing. Finally,additional pressurized gas may be vented to allow the piston 252 toreturn to its retracted position, thereby allowing locking clutch 92 tomove from the intermediate position to the locked position under thebiasing force of the second biasing member 98. As a result, the axleshaft 24 may be mechanically coupled to the hub assembly 88 via thelocking clutch 92 such that torque is transmitted between the axle shaft24 and the hub assembly.

It is further noted that for a locking clutch actuator 94 having apneumatic or hydraulic configuration, the friction clutch 90 and lockingclutch 92 will move to or remain in the disengaged and locked positions,respectively when a sufficient amount of pressurized fluid cannot beprovided to actuate the piston, such as in the event of a leak,performance issue with the pressurized gas source 256, or a supply valvethat cannot be actuated from a closed position. As such, the wheel endassembly will default to a connected state in which an axle shaft 24 isoperatively connected to a hub assembly 88 to facilitate thetransmission of torque therebetween.

Referring to FIGS. 12-14, another configuration of a wheel end assembly26′ is shown. This configuration is similar to the configurationpreviously discussed, but includes two pistons that can be independentlyactuated to independently move a friction clutch and a locking clutch.As such, the friction clutch and the locking clutch may be spaced apartfrom each other at all actuation positions and the locking clutch maymove between unlocked and locked positions without pausing at anintermediate position.

Referring to FIG. 12, the axle assembly 10 is shown with the frictionclutch 90 in an engaged position and the locking clutch 92 in a lockedposition. Torque may be transmitted between the axle shaft 24 and thehub assembly 88 via the friction clutch 90 when the friction clutch 90is in the engaged position. In the engaged position, the locking clutch92 may be biased away from the friction clutch 90 under the biasingforce of the second biasing member 98, and the first biasing member 96may exert a biasing force on the actuation plate 194 that actuates theactuation plate 194 toward the locking clutch 92 to compress and engagethe disc pack 190. In the configuration shown, the inner friction discs200 of the friction clutch 90 may be coupled to the axle shaft 24, suchas with mating splines, and the disc pack hub may be eliminated. Inaddition, the first biasing member 96 is depicted as a coil spring thatextends from the actuation plate 194 to the hub cap 110. Torque may alsobe transmitted between the axle shaft 24 and the hub assembly 88 via thelocking clutch 92 when the locking clutch 92 is in the locked position.In the locked position, the second biasing member 98 exerts a biasingforce on the locking clutch 92 that actuates the locking clutch 92 awayfrom the friction clutch 90 so that the locking clutch gear 242 mesheswith the hub gear 166 of the hub assembly 88. As such, torque may betransmitted between the axle shaft 24 and the hub assembly 88 by way ofthe meshed teeth of the locking clutch gear 242 and the hub gear 166.The locking clutch actuator 94 may be disposed in a retracted positionin which the locking clutch actuator 94 does not exert sufficient forceon the locking clutch 92 to overcome the biasing force of the secondbiasing member 98, such as when pressurized gas is not provided to thepiston housing 250.

The locking clutch actuator 94 may include a piston housing 250′ thatmay include separate recesses that may receive an outer piston 300 andan inner piston 302. The recesses may not be fluidly connected, whichmay allow the inner piston 302 to be actuated independently of the outerpiston 300. Each recess may be selectively fluidly connected to thepressurized gas source 256 via separate passages in the piston housing250′, separate conduits that extend from the piston housing 250′, orboth. The outer piston 300 may be disposed further from the axis 50 thanthe inner piston 302. In addition, the outer piston 300 may extendcontinuously around the inner piston 302. The outer piston 300 may beconfigured to actuate the friction clutch 90 via one or more rods 304that may extend between the outer piston 300 and the friction clutch 90.The rod 304 may be positioned further away from the axis 50 than thelocking clutch 92 and may extend through openings in the inner frictiondiscs 200 and the outer friction discs 202 of the disc pack 190 andextend to the actuation plate 194. A thrust bearing 260 may be providedbetween the outer piston 300 and an end of the rod 304 to facilitaterotational movement of the rod 304 with respect to the outer piston 300.

Referring to FIG. 13, the axle assembly 10 is shown with the frictionclutch 90 in the engaged position and the locking clutch 92 in theunlocked position. In the unlocked position, the inner piston 302 isactuated toward the friction clutch 90 or to the left from theperspective shown such that the locking clutch gear 242 disengages fromthe hub gear 166 of the hub assembly 88. As such, torque may not betransmitted between the axle shaft 24 and the hub assembly 88 via thelocking clutch 92 when the locking clutch 92 is in the unlockedposition. For example, pressurized fluid may be provided to actuate theinner piston 302 from its retracted position such that the lockingclutch 92 moves from the locked position to the unlocked position.

Referring to FIG. 14, the axle assembly 10 is shown with the frictionclutch 90 in a disengaged position and the locking clutch 92 in theunlocked position. Torque may not be transmitted between the axle shaft24 and the hub assembly 88 via the friction clutch 90 when the frictionclutch 90 is in the disengaged position or insufficient torque may betransmitted from the axle shaft 24 to the hub assembly 88 via thefriction clutch 90 to rotate the hub assembly 88 when the frictionclutch 90 is in the disengaged position. In the disengaged position, theouter piston 300 may exert force against a first end of the rod 304,which may actuate the rod 304 toward the hub cap 110. Force may betransmitted from the rod 304 to the actuation plate 194 and may overcomethe biasing force exerted by the first biasing member 96 to actuate theactuation plate 194 toward the hub cap 110, or to the left from theperspective shown in FIG. 14, to decompress, release, or disengage thediscs of the disc pack 190. As such, no torque or insufficient torquemay be transmitted between the axle shaft 24 and the hub assembly 88 viathe friction clutch 90 when the friction clutch 90 is in the disengagedposition. Movement of the actuation plate 194 to the left from theconfiguration shown may allow the discs of the disc pack 190 to moveapart and may compress the first biasing member 96. As such, the hubassembly 88 may be rotatable with respect to the axle shaft 24 when thefriction clutch 90 is in the disengaged position and the locking clutch92 is in the unlocked position.

The axle shaft 24 may be reconnected to the hub assembly 88 byeffectively reversing the sequence of steps described above. Forinstance, pressurized gas may be vented to allow the outer piston 300 toretract. The actuation plate 194 and the rod 304 may move from theirprevious positions to the right from the perspective shown to compressand reengage the discs of the disc pack 190 under the biasing force ofthe first biasing member 96. As a result, torque may be transmittedbetween the axle shaft 24 and the hub assembly 88 via the frictionclutch 90. The locking clutch 92 may be held in the unlocked positionuntil the rotational velocity of the hub assembly 88 is sufficientlyclose to the rotational velocity of the axle shaft 24 as previouslydiscussed. Finally, pressurized gas may be vented to allow the innerpiston 302 to return to its retracted position, thereby allowing lockingclutch 92 to move from the unlocked position to the locked positionunder the biasing force of the second biasing member 98. As a result,the axle shaft 24 may be mechanically coupled to the hub assembly 88 viathe locking clutch 92 such that torque is transmitted between the axleshaft 24 and the hub assembly.

The axle assemblies and methods of control described above may beprovided with an axle system that has drive axles that may be connectedin series, such as a tandem axle arrangement. Efficiency of the axlesystem may be improved by not providing torque to the wheels of at leastone drive axle when torque demands are sufficiently low, such as whenthe vehicle is at a road cruise speed, such as cruising at highwayspeeds. As such, the wheel end disconnect described above may allow suchefficiency gains to be realized. In addition, the method of control mayallow the wheel end disconnect to be reengaged by engaging the frictionclutch prior to engaging the locking clutch to reduce the rotationalvelocity differences between the axle shaft and the hub assembly so thatthe locking clutch may be reengaged without mechanical clashing ormisalignment between the base gears or with reduced mechanical clashing,thereby reducing noise and improving durability and operationalperformance.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

What is claimed is:
 1. An axle assembly comprising: a hub assembly thatis rotatable about an axis; an axle shaft that is received in the hubassembly and is rotatable about the axis; a friction clutch that isreceived in the hub assembly and is moveable between an engaged positionin which torque is transmitted between the axle shaft and the hubassembly via the friction clutch and a disengaged position; and alocking clutch that is received in the hub assembly and that isrotatable about the axis with the axle shaft, wherein the locking clutchis moveable between a locked position in which the locking clutchtransmits torque to the hub assembly and an unlocked position in whichthe locking clutch does not transmit torque to rotate the hub assembly.2. The axle assembly of claim 1 wherein the hub assembly is rotatablewith respect to the axle shaft when the friction clutch is in thedisengaged position and the locking clutch is in the unlocked position.3. The axle assembly of claim 1 wherein the friction clutch includes adisc pack and an actuation plate that is rotatable about the axis withthe axle shaft and is moveable in an axial direction with respect to theaxle shaft to actuate the disc pack.
 4. The axle assembly of claim 3further comprising a first biasing member that biases the actuationplate toward the locking clutch to urge the friction clutch toward theengaged position.
 5. The axle assembly of claim 4 further comprising asecond biasing member that biases the locking clutch toward the lockedposition, wherein the second biasing member is disposed on an oppositeside of the actuation plate from the first biasing member.
 6. The axleassembly of claim 5 wherein the second biasing member extends from thelocking clutch toward the actuation plate.
 7. An axle assemblycomprising: a hub assembly that is rotatable about an axis; an axleshaft that is received in the hub assembly and is rotatable about theaxis; a friction clutch configured to transmit torque between the axleshaft and the hub assembly, wherein the friction clutch is moveablebetween an engaged position and a disengaged position; and a lockingclutch configured to transmit torque between the axle shaft and the hubassembly, wherein the locking clutch is moveable between a lockedposition and an unlocked position in which the locking clutch does nottransmit torque to rotate the hub assembly, and the locking clutchactuates the friction clutch to the disengaged position when the lockingclutch moves to the unlocked position.
 8. The axle assembly of claim 7wherein the locking clutch is spaced apart from the friction clutch whenthe locking clutch is in the locked position and the locking clutchengages the friction clutch when the locking clutch is in the unlockedposition.
 9. The axle assembly of claim 7 wherein the locking clutchmoveable to an intermediate position that is axially positioned betweenthe locked position and the unlocked position, wherein the lockingclutch actuates the friction clutch to the disengaged position when thelocking clutch moves from the intermediate position to the unlockedposition.
 10. The axle assembly of claim 9 wherein the locking clutchdoes not transmit torque to the hub assembly and the friction clutchtransmits torque to the hub assembly when the locking clutch is in theintermediate position.
 11. The axle assembly of claim 9 furthercomprising a locking clutch actuator that is operable to actuate thelocking clutch from the locked position to the intermediate position andto the unlocked position.
 12. The axle assembly of claim 11 wherein thelocking clutch actuator actuates the locking clutch toward the frictionclutch.
 13. The axle assembly of claim 12 wherein the axle assemblyincludes a housing assembly, a piston housing that is disposed in thehub assembly and is fixedly disposed on the housing assembly, and apiston that is moveably disposed in the piston housing that actuates thelocking clutch.
 14. The axle assembly of claim 13 wherein the lockingclutch is partially received between the piston and the axle shaft. 15.The axle assembly of claim 13 further comprising a thrust bearing thatis axially positioned between the locking clutch and the piston thatfacilitates rotation of the locking clutch with respect to the piston.16. A method of controlling an axle assembly comprising: disconnectingan axle shaft from a hub assembly that is adapted to support a wheel by:actuating a locking clutch from a locked position in which the lockingclutch transmits torque to the hub assembly to an intermediate positionin which the locking clutch does not transmit torque between the axleshaft and the hub assembly; and actuating the locking clutch from theintermediate position to an unlocked position in which the lockingclutch actuates a friction clutch from an engaged position in whichtorque is transmitted between the axle shaft and the hub assembly viathe friction clutch and a disengaged position in which torque is nottransmitted between the axle shaft and the hub assembly via the frictionclutch.
 17. The method of claim 16 further comprising connecting theaxle shaft to the hub assembly by: actuating the friction clutch fromthe disengaged position to the engaged position by actuating the lockingclutch from the unlocked position to the intermediate position, therebyallowing torque to be transmitted between the axle shaft and the hubassembly; and actuating the locking clutch from the intermediateposition to the locked position to mechanically couple the axle shaft tothe hub assembly with the locking clutch such that torque is transmittedbetween the axle shaft and the hub assembly via the friction clutch. 18.The method of claim 17 wherein a first biasing member biases thefriction clutch from the disengaged position to the engaged position anda second biasing member biases the locking clutch from the unlockedposition to the intermediate position and from the intermediate positionto the locked position.
 19. The method of claim 17 wherein the lockingclutch is held in the intermediate position before moving to the lockedposition.
 20. The method of claim 19 wherein the locking clutch is heldin the intermediate position until a rotational velocity of the hubassembly is within a threshold amount from a rotational velocity of theaxle shaft.